Note: Descriptions are shown in the official language in which they were submitted.
3~ 1
METHOD OF MAKING COKE IN A COKE OVEN BATTERY
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to a method of making
coke in coking chambers of a coke-oven battery and
is particularly concerned with the control of the
combustion gas supply to the burners of the battery.
The invention also provides a method of measuring
the temperature of hot coke.
2~ DESCRIPTION OF THE PRIOR ART
A coke-oven battery has a number of coking
chambers. Between each pair of adjacent coking
chambers 9 there is a combustion wall containing a
plurality of combustion chambers. Combustion of gas
takes place in the combustion chambers to provide
the heat required for the coking process. A battery
may have a great many, e.g. in the order of a
thousand, combustion chambers. Below the coking
chambers and the combustion ~hambers there are
regenerators in which waste heat from the burned
combustion gases is used to heat the incoming
combustion air. Each regenerator is periodically
switched over from heating air to being heated by
hot gases.
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In the preparation of coke, by a batch
process, coking coal is dry-distilled in the coking
chamber for a period of time called the coking time.
During the coking time, the temperature of the
charged load of coal, hereinafter called coke cake,
rises more rapidly near the combustion walls than in
the middle. The coke cake is pushed out of the
coking chamber after the expiry of the coking time ~
(this operation is called pushing) and transferred ~¦
to a quenching car via a so-called coke guide. Then ~¦
the hot coke is conveyed in the quenching car to a
quenching installation and quenched with water.
The control of the heat supply in the coking
process can be considered at three levels, going
from the smaller scale to the larger:
- the combustion chamber level
- the combustion wall level
- the battery level.
At the combustion chamber level what matters
is that each combustion chamber should have the
right temperature with respect to ~he other
combustion chambers of the same combustion wall.
This is a matter of a correct distribution of gas
between the combustion chambers of a combustion
wall. Correction of a combustion chamber is an
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incidental operation and is effected by the
readjustment of louvre bricks and cleaning or repair
of the refractory structure.
At the combustion wall level what matters is
that each combustion wall should have the right
temperature with respect to the other combustion
walls of a battery. This is a matter of a correct
distribution of gas between the combustion walls of
a battery. Correction of a combustion wall is
effected by adjustment of the gas supply, e.g. using
a diaphragm valve, cleaning of supply lines, shut-
off valves etc.
At the battery level it is a matter of
supplying the correct amount of heat. Correction is
effected by adjustment of the total quantity of gas.
The temperature of the coke cake rises during
the coking time. During the operation of the
battery, a pushing sequence is used, e.g. for five
chambers the order 1-3-5-2-4. The coking chambers
are thus filled and pushed in a certain sequence.
As a result, the state at any moment of the coking
processes in the different coking chambers is very
varied. Finally the temperature of parts of the
coking battery structure varies due to the periodic
switching over of the regenerators. In controlling
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the coking process, use is made of temperature
measurements carried out on the coke-oven battery
structure. In interpreting the results of these
temperature measurements, allowance must be made for
the above-mentioned temperature cycles and this
makes the control of the coking process at the three
levels mentioned above more difficult.
For many years temperatures in the combustion
chambers have been measured for the purpose of
control of the coking process, using an optical
pyrometer. The difficulty with this measuring
method is the low accuracy of the r~sult. The
measurement is really only useful for control at the
combustion chamber level when nothing better is
available.
GB-A~1,393 9 011~ describes a method of the
control of the battery temperature, in which it is
sought to maintain a time-averaged costant value of
the battery temperature. In this method the
temperature of the regenerator checkerwork is
measured and held constant by adjusting the gas
supply This control at battery level is an open
regulation of the coke temperature at the end of the
coking time. FR-A-2,318,918 describes a method of
combustion control of the same type, in which flue
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temperatures are measured.
From EP-A-0025630 it is known to measure the
temperature of the coke in the quenching car using
an infrared sensor. During the transfer of the coke
from the coking chamber to the quenching car, the
coke is distributed along the length of the
quenching car from the coke side towards the machine
side (these are the two sides of the battery). The
coke cake collapses vertically, so that the
temperature differences in the vertical and width
direction of the coke cake are evened out. In the
~, method disclosed in EP-A-25630 the measurement of
coke temperature in the quenching car is used for
the location and adjustment of combustion walls with
a deviant mean temperature (control at the
combustion wall level) and for locatlon and
adjustment of combustion chambers with a deviant
temperature (control at the combustion chamber
level). The infrared sensor measures the surface
temperature of the coke in the quenching car. Its
aperture angle and height above the quenching car
are such that it views a substantial part of the
width of the coke in the quenching car~
Expert opinion has been that it is desirable
to aim to keep the temperature constant at the
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levels of the combustion chamber, combustion wall
and battery. A difficulty in this strategy is that
the temperature of the coke cakes at pushing varies
considerably.
SUMMARY OF THE INVENTION
The object of the invention is to provide a
method of making coke in a coke oven battery which
achieves improved control of the coke temperature at
the end of the coking time.
Another object of the invention is to provide
an improved method for measuring the temperature of
coke.
According to the invention there is provided
a method comprising the following steps:
a) measuring the coke temperature after pushing
of the coke out of a coke-oven into the quenching
car and before quenching using at least one infrared
sensor,
b) determining a value corresponding to the
di~ference between the temperature of the coke in
the quenching car and a predetermined reference
value for the temperature of the coke at the end of
the coking time,
c) determining the mean of a series of said
difference values relating to the coke loads
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obtained from a series of coke ovens and
d) adjusting the combustion gas supply to the
burners of at least a plurality of coking chambers
of the coke-oven battery in dependence on said mean
of the difference values.
The reference value for the temperature at
the end of the coking time must be chosen with
various factors in mind:-
i) with a higher reference value the emission of
e.g. gas and smoke on pushing of the coke is lower;
ii) the quality of the coke produced is dependent
on the reference value;
iii) with a lower reference value less energy
(i.e. less gas) is used;
iv) with a given maximum heat load on the coke-
oven battery structure, coke production is higher
with a lower reference value.
Another critical factor however is the
temperature at which the coke cake has undergone
su~ficient shrinkage to prevent high forces on the
combustion walls and the struts during the pushing
- operation. The reference value is chosen to be as
low as possible and is preferably equal to the
temperature at which the coke cake has undergone
sufficient shrinkage, with an added margin to allow
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for the standard deviation of the actual coke
temperature at pushing.
The method according to the invention, as a
result of which the coke is prepared with a
temperature at the end of the coking time falling
within a narrow range has various advantages:-
i) undesirable emissions during pushing can be
largely prevented,
ii) coke of a uniform quality can be obtained,
iii) the coke can be pushed at the end of the
coking time with a lower temperature on average, so
that less energy is used in the overall running of
the battery 3
iv) high forces on the combustion walls and the
struts due to too low a coke temperature at pushing,
and consequent wear and damage, can be prevented, so
that a longer battery life can be achieved.
As has been remarked above, temperature
differences over the height and width of the coke
cake are evened out during the transfer of the coke
into the quenching car. The temperature measured in
the quenching car with the infrared sensor is hence
after processing representative of the mean
temperature of the coke at the end of the coking
time. Allowance can be made during further
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processing of the measurement value for any
temperature variations measured over the length of
the quenching car which correspond to variations in
the temperature of the coke cake from coke to
machine side.
By adjusting the gas supply on the basis of a
mean of difference values, the effect on the gas
supply to a number of coke ovens of a coke-oven with
a strongly deviant coke temperature at the end of
the coking time is smoothed out. On the other hand
systematic deviations of the coke temperature at
pushing for the series of coke ovens is corrected by
adjusting the gas supply at effectively the battery
level.
The temperature of the coke in the quenching
car can be measured with one or more infrared
sensors.
It appears that the surface of the coke in
the quenching car has cooled off to some extent at
the time of measurement with infrared sensors.
Preferably therefore the temperature of the coke
load or pile in the quenching car is measured under
the surface of the coke pile as seen in the gaps
between the coke lumps using an infrared sensor
having a narrow measuring aperture angle.
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Preferably this aperture angle (or sensing angle) is
such that the measuring spot of the infrared sensor
at the location of the surface of the coke in the
quenching car is less than 100 mm in width, more
preferably less than 40 mm in width. The
temperature of the coke in the quenching car is thus
measured below the cooled surface, and the measured
temperature is largely independent of the extent of
cooling of the coke surface. This cooling varies as
a function of the distance between the coke oven
from which the coke came and the measuring point.
For the purpose of eliminating temperature
variations of the coke in the quenching car
resulting from the deviation of the actual coking
time from the planned coking time, the measured
temperature of the coke in the quenching car is
preferably corrected after measurement for deviation
of the actual coking time relative to the planned
coking time. Use is here made of a relationship
be~ween the temperature of the coke at the end of
the coking time and the length of the coking time.
A determination is made before the difference from
the target value is determined of what the
temperature of the coke was, or would have been, at
the end of the planned coking time for a coking time
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which is longer, or shorter, than planned. This
makes the method of the invention more effective.
It is preferred that the adjustment of the
gas supply takes place according to the invention
for the burners belonging to a considerable number
of coke ovens. Gas supply and combustion gas
removal arrangements common to all the coke ovens of
a battery are often present. In that case, it is
preferred to adjust the supply of gas to the burners
belonging to all the coke-ovens of the battery
simultaneously.
The series of coke-ovens for which
measurements of coke temperature are made can be
chosen in various ways. Thus for instance a mean of
difference values can be determined for those coke-
ovens of a battery which are discharged during a
shift~ and the gas supply adjusted on the basis of
this difference. The series can however be chosen
in relation to the pushing sequence. In the latter
case, it is practical to determine the mean of
differences per series of pushed coke-ovens and
adjust the gas supply after the discharge of the
series. The series can be fewer than the total
number of coke-ovens in the battery.
In a practical embodiment of the invention
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the method is applied in a master-slave system, in
which the gas supply to the burners is in addition
adjusted using a conventional feedback control
method, e.g. on the basis of a temperature measured
in the coke-oven battery structure, e.g. the
regenerator temperature. In this case the
conventional feedback control method is adjusted on
the basis of the mean of difference values in
accordance with the invention.
In another aspect, the invention provides a
method for measuring the temperature of a hot coke
pile of coke lumps using at least one infrared
sensor, in which the temperature of the hot coke is
measured under the surface of the coke pile as seen
in the gaps between the coke lumps using an infrared
sensor having a narrow measuring aperture angle.
Suitably this aperture angle is such that the
measuring spot at the location of the surface of the
coke is less than 100 mm in width and more
preferably less than 40 mm in width. This method of
measurement is applicable to any pile or body of hot
coke lumps. The term pile is used generally, to
include a body of coke in a vessel, e.g. a quenching
car.
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BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention, and
a non-limitative example thereof, will now be
described with reference to the accompanying
drawings, in which:-
Fig. 1 is a graph representing the progress
of the temperature of coke in a coke-oven during the
coking time.
Fig. 2 is a diagram illustrating the
adjustment of the gas supply according to the
invention.
Fig. 3 is a diagram illustrating the
adjustment of the gas supply according to a specific
embodiment of the method.
Figs. 4 and 5 show frequency distributions
for the temperature of the coke in the quenching
car~
DESCRIPTION OF THE PREFERRED EMBODIMENT
In Fig. 1 the progress of the temperature T
of coke during the coking time t is given for the
middle of the coke cake (line A) and the coke cake
immediately adjacent to the combustion walls (line
B). To is a ref`erence value for the coke
temperature at the end of the coking time. It can
be seen from the graph that the line B at the end of
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14.
the coking time has a smaller slope than line A.
The measurement of the temperature of the edge of
the coke cake is not so good, as a measure of the
temperature at the end of the coking time, as the
temperature of the coke in the quenching car.
In the diagram of Fig. 2, there is
diagrammatically shown a coke-oven battery 1, the
coke-ovens of which are filled in the direction
indicated by the arrow 2 with coking coal. At the
end of the coking time the coke is pushed in the
direction of the arrow 3 and transferred to the
quenching car 4. The energy required for the coking
process is obtained by the combustion of gas
supplied to the coke-oven battery in the direction
of arrow 5. The combustion gases are brought to the
stack 7 along the direction indicated by arrow 6.
The temperature T of the coke from each coke-
oven is measured after pushing into the quenching
car 4 using an infrared sensor 8. A correction 9 is
applied to the temperature of the coke thus measured
at the end of the actual coking time, leading to the
determination of a corrected temperature T'
appropriate to the planned coking time. The supply
of gas 5 via valve 11 is adjusted using the control
device 10 on the basi~ of a ~ean value of the
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differences between the corrected temperature T' of
the coke in the quenching car and the reference
value To for a series of coke loads pushed from a
series of coke-ovens.
In practice, the method most appropriate for
the adjustment of the gas supply is a variation of
the so-called pause period during switching over of
the regenerators.
Because of the high thermal capacity of the
coke-oven battery structure, it is not practical to
adjust the gas supply on the basis of the coke
temperature measured in the quenching car after each
pushing operation of a coke-oven. A good practice
is to adjust the gas supply after the pushing of the
coke-ovens which belong to the same series in the
pushing sequence in operation or at the end of a
shift, and on the basis of the mean value of the
differences of the coking temperature measured in
the quenching car and the reference value To of all
coke ovens of the series or of all the coking
chambers which have been pushed during the shift.
The coke temperature measured in the
quenching car appears to be a good starting point
for adjusting the gas supply to the battery in the
event of machine failure and when changing the
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planned coking time of a battery.
The coke temperature in respect of each coke-
oven as measured in the quenching car is also a good
means of locating variations in the coking chambers.
On this basis the control of the coking process can
take place at the level of the combustion wall by
correction of the supply of gas by adjustment of the
gas supply using a diaphragm valve and by cleaning
the gas supply line.
Fig. 3 shows a specific embodiment of the
method in which the gas supply 5 is adjusted using
the control device 10 and valve 11, on the basis of
for instance a temperature Tc measured in the coke-
oven battery structure, e.g. the so-called
regenerator temperature, where this control is
adjusted on the basis of the mean value of the
differences between the corrected temperature T' of
coke in the quenching car and the reference value
To.
Example
This example refers to a coking plant with
108 identical coke-ovens (coking chambers) with a
height of six and a half meters. The coking plant
is divided into four identical coke-oven batteries
21,22,23 and 24 each with twenty seven coke-ovens.
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17.
The method according to the invention was introduced
for these batteries. The temperature at which the
coke cake has adequate shrinkage is 1020C for the
mixture of coal employed. The reference temperature
To for the temperature of the coke at the end of the
coking time was established at 1050C. The planned
coking time was eighteen hours. The temperature of
the coke in the quenching car was measured with an
infrared sensor with a measurement spot of 20 mm at
the location of the upper surface of the pile of
coke in the quenching car.
The temperatures of the coke measured in the
quenching car before adjustment of the supply of gas
on the basis of the difference from the reference
value, i.e. before application of the method of the
invention, can be summarised as follows:
TABLE I
Battery Temperature of coke in quenching car
Mean value (C) Standard deviation (C)
21 1023 43
22 1054 27
23 995 39
2l~ 1020 40
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Fig. 4 shows a frequency distribution related
to the results of Table I with, along the horizontal
axis, the temperature T in C of the coke as
measured in the quenching car and, along the
vertical axis, the number of coke ovens n. It can
be seen that
i) the Mean value of the coke temperature of the
batteries deviates by almost 60C.
ii) the standard deviation is about 40C.
After the introduction of the method of the
invention the following results were achieved. I
TABLL II
Battery Temperature of coke in quenching car
Mean value (C) Standard deviation (C)
21 1051 29
22 1040 26
23 1041 25
24 1049 22
The related frequency distribution is
reproduced in Fig. 5, which should be compared with
Fig. 4. It can be seen that
i) the mean value of the final coke temperatures
of the batteries is very close to 1050C.
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ii) the standard deviation is reduced to about
25C.
Thus in this Example a substantial
improvement is achieved.
